Solvent extraction of metals with a cyclic alkylene carbonate

ABSTRACT

Cyclic organic carbonates have been found, along with mixtures of same with other organic liquids that are miscible therewith, to extract the following metals in stable complex or simple salt form from a medium in which the solvent is not completely soluble. Extractable metals include gold, platinum, palladium, rhodium, iridium, cobalt, copper, vanadium, uranium, bismuth, cadmium, mercury, and cerium.

United States Patent [191 Stephens 1 Oct. 14, 1975 SOLVENT EXTRACTION OFNIETALS WITH A CYCLIC ALKYLENE CARBONATE [75] Inventor: Bobby G.Stephens, Spartanburg,

[73] Assignee: Wellington M. Manning, Jr.,

Spartanburg, S.C.

22 Filed: July 11, 1972 21 Appl. No.: 270,686

[52] US. Cl. 423/8; 23/312 ME; 423/21;

423/22; 423/24; 423/63; 423/87; 423/99; 423/139 [51] Int. Cl BOld 11/00[58] Field of Search 423/8, 21, 22, 24, 63,

423/87, 99, 139; 260/4291, 340.2, 430, 438.1, 439 R, 447; 23/312 ME [56]References Cited UNITED STATES PATENTS 2,688,645 9/1954 Badertscher etal 260/3402 12/1959 Seaborg 423/8 10/1964 Kormendy et a1. 260/3402Primary ExaminerLeland A. Sebastian Assistant ExaminerE. A. MillerAttorney, Agent, or Firm-Wellington M. Manning, Jr.

[ ABSTRACT 29 Claims, No Drawings SOLVENT EXTRACTION OF METALS WITH ACYCLIC ALKYLENE CARBONATE BACKGROUND OF THE INVENTION Numeroustechniques have heretofore been devised for the reclamation of metalsfrom naturally occuring ores containing same. For the most part,disadvantages exist with each of these processes from the standpoint ofeconomics of the process, purity of the metal obtained, toxicity of thematerials utilized in the process, difficulty of recovery of the puremetal, and the like.

A conventional process for mining gold for example is to treat the orewith sodium cyanide to dissolve the gold; add zinc powder to the leachwater to form a gold-silver amalgamation if silver is present; treat theamalgam with nitric acid to dissolve the silver; recover the gold fromthe solution, and refine the gold. Likewise, aqua regia has been used todissolve the gold, followed by treatment with ferrous sulfate toprecipitate a spongy gold. The spongy gold is then recovered and refinedin what is referred to as a problematical procedure. With other metalsalso, techniques are as troublesome and expensive. Moreover, thepresence of certaiin tramp metals tremendously decrease the efficiencyof the processes.

The present invention provides a solvent group that extracts metals in agreatly improved manner than those heretofore known, along with aprocess for using same. The problems of the prior art are avoided, thusimproving mining and refining techniques for commercial miningoperations.

While the prior art is replete with various and sundry techniques forimproving mining and refining processes for metals, there is no knownprior patented art directed to the present invention. Cyclic organiccarbonates have heretofore been used for several purposes. For example,the extraction of iron three and as a tris(pentan-2,4-dione)-iron (III)from aqueous solution for the spectrophotometric determination wasreported in Analyst, March 1971, Volume 96, page 230-234; extraction ofthe 1,10-phenanthroline, 4-7-diphenyl-1, IO-phenanthroline and2,4,6-tripyridyl-sym-triazine complexes of iron (II) into propylenecarbonate was reported in Analytical Chemistry, Volume 39, October 1967,page 1478-1480 and a technical bulletin on propylene and ethylenecarbonate in particular was published by Jefferson Chemical Company,Houston, Texas in 1960. None of these publications teach or suggest theuse of the cyclic organic carbonates as solvents for metals as discussedhereinafter.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a novel solvent for extraction of metals from media containingsame.

A further object of the present invention is to provide a novel solventfor the extraction of gold, platinum, palladium, rhodium, iridium,cobalt, copper, vanadium, uranium, bismith, cadmium, mercury, andcerium, from media containing same.

Still another object of the present invention is to provide a novelprocess for the recovery of valuable metals from naturally occuring orescontaining same.

Generally speaking the present invention is directed to the use ofcyclic organic carbonates as solvents for the solvent extraction ofmetals selected from the class consisting of gold, platinum, palladium,rhodium, iridium, cobalt, copper, vanadium, uranium, bismuth, cadmium,mercury, and cerium.

More specifically, the cyclic organic carbonates for use in solventextraction of metals according to the present invention are preferablypropylene carbonate (4-methyl dioxo1one-2) and ethylene carbonate(dioxolone). Ethylene carbonate must be used in conjunction with anotherorganic liquid in which it is miscible since ethylene carbonate iscompletely soluble in water. Likewise, all of the cyclic organiccarbonates may be used as mixtures with other organic liquids miscibletherewith and immiscible or only slightly soluble in themetal-containing medium, generally water. Propylene carbonate isapproximately 20 per cent soluble in water. Hence, it also may bepreferably employed in conjunction with a solvent carrier to, amongother things, reduce its solubility in water. In fact, the solventmixture may be preferred due to economics and ease of concentration ofthe extract for recovery of the pure metals therefrom.

The process of the present invention for the solvent extraction of metalcomprises the steps of contacting a medium containing the metal inextractable form with a cyclic organic carbonate, removing the extract,and separating the metal from the extract.

More specifically, the process of the present invention involves thedissolving of the desired metal from ores or other media containingsame, if necessary. In certain circumstances, the metal will then be inextractable form as a stable complex or simple salt in an aqueoussolution or may be further treated to be in suitable extractable form.The cyclic organic carbonate solvent can then be brought into contactwith metal containing medium and agitated. The metal complex or saltwill be extracted by the solvent, generally in a large percentage ofthat present. Thereafter, the metal-containing extract is separated fromthe medium, generally an aqueous layer and the metal recovered from theextract.

Dissolution of the metal may be accomplished by known techniques. Forexample aqua regia may be used to dissolve gold from gold bearing ores,whereby the gold appears as AuCl; or perhaps HAuCL, in the leach water.The chloride may then be directly extracted by one of the carbonates ofthe present invention. Likewise, chlorine gas can be brought intocontact with the gold to form the chloride for extraction. The othermetals listed herein may be handled similarly to arrive at a suitableextractable form of the metal in the solution or some other media, suchas a concentrate.

The cyclic organic carbonate may be used alone or in admixture with someother organic liquid that is miscible with the carbonate, but immiscibleor no more than slightly soluble in the metal carrying medium. Generallyany proportion from at least about 5 per cent carbonate is successful inextracting the metal. Depending upon the particular carbonate-diluentmixture, the specific gravity of the mixture may be greater or less than1.0, whereby certain solvent compositions sink and others float, bothcarrying the extracted metal. Further, when utilizing a solvent carrieror diluent for the cyclic organic carbonate, it may be quite desirableto remove the diluent prior to recovery of the metal from the extract.Benzene, for example, serves as an excellent diluent due to thedifference in boiling point from the carbonate and due to the lowness ofthe boiling point of benzene (80.1C.). Hence a solution of per centbenzene and 5 per cent propylene carbonate may be employed to extractthe metal. Thereafter, the benzene may be flashed off, leaving the metalin the propylene carbonate. A highly concentrated form of extract isthus provided for reduction of the metal salt or complex to the metalform by electrowinning, or the like or precipitation of the metal saltfollowed by conversion of the precipitated salt to the pure metal.

A large number of metals are discussed herein as suitable for solventextraction by a cyclic organic carbonate solvent. In general, the merepresence of these metals may be determined colorimetrically by visualobservation of the extract with the metal contained therein. Gold andplatinum, for example, impart a yellow color to the extract, rhodium alight red and iridium a deep red. Thus the carbonates of the presentinvention may also be utilized in the prospecting sense to enable one toalmost immediately ascertain the presence of a particular metal beingsought by a quick, but reliable analysis of an ore sample.

Insofar as the large group of metals is concerned, optimum conditionsfor each varies. The majority of optimization has been' directed towardthe recovery of gold. As such, much of the discussion herein is directedto gold recovery techniques. By routine investigation, however, optimumtechniques for the metals not discussed in detail may be ascertained.Hence the best complex or salt of the metal; the pH range forextraction; the desirability of the carbonate only or a solvent mixtureas the extract; and if a mixture, the best diluent and percentagethereof; and the like may be determined for each metal by routineexperimentation based on the teachings set forth herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Metals selected from the classconsisting of gold, platinum, palladium, rhodium, iridium, cobalt,copper, vanadium, uranium, bismuth, cadmium, mercury, and cerium, havebeen found to be extractable in stable complex and/or simple salt formfrom a medium containing same by a cyclic organic carbonate solvent.Extraction as taught herein may be conducted in a mining process toclaim the pure metal from the naturally occuring ores containing same;in a refining process where a concentrate of the metal containing mediumis furnished; and in a metal reclamation process where scrap metaland/or materials are treated to reclaim valuable, reuseable constituentsthereof.

Preferred cyclic organic carbonates are propylene carbonate (4-methyldioxolone-2) and ethylene carbonate (dioxolone). Further, it has beendetermined that organic liquids miscible with the carbonate may be usedas diluents or carrier solvents if they are immiscible or no more thanslightly soluble in the metal containing medium. In fact, ethylenecarbonate is completely miscible in water, and for use according to theteachings of the present invention must be employed in conjunction withone of the solvent carriers. In the mixed form, the ethylene carbonateloses its miscibility with water and satisfactorily extracts the metalcomplex or salt without appreciable solvent loss. Immiscibility of thesolvent carrier does not necessarily infer complete insolubility inwater, but also refers to liquids that are no more than slightly solublein the medium. Exemplary of suitable solvent carriers without limitationthereto are benzene, o-xylene, m-xylene, p-xylene,

diethyl ether, 4-methyl-2-pentanone, 2,4-pentandione, ethyl acetate,n-heptyl alcohol, chloroform, and the like. Further, it has been foundthat suitable extraction is obtained in volume mixtures containing fromat least about 5 per cent of the cyclic organic carbonate with thebalance being solvent carrier.

A further important feature of extractability with the cyclic organiccarbonates is the particular means of removing the extract containingthe metal from the original medium, where the medium is water. Propylenecarbonate, which is the preferred cyclic organic carbonate has aspecific gravity of 1,283 at 20/20C. The metal containing extract willtherefore pass through the water and become a bottom layer of a twolayer solution. Propylene carbonate is, however, about 20 per centsoluble in water. As such, approximately 20 per cent of the solvent islost, though it may be recovered by the later addition of benzene or oneof the aforementioned solvent carriers. The procedure may be reversed,however, by mixture of one of the diluents with the propylene carbonate.Benzene, for example, mixed with the propylene carbonate also extractsthe metal. The specific gravity of the propylene carbonatebenzenemixture may be less than 1.0, depending upon the ratio of theconstituents, whereby the extract containing the metal forms the topphase of the two phase system. Hence, depending upon the needs of theparticular process, the metal to be extracted may be carried to thebottom or the top of the water medium for removal. Thereafter, themetal-pregnant extract may be separated from the water or other liquidmedium by conventional separation techniques, dependent upon theposition of the extract phase.

The particular metal or metals to be recovered should be in a stableform to be removed by the solvent. For example, gold, platinum,palladium, iridium, rhodium, and uranium may be suitably removed ashalides, thiocyanates and the like over a wide pH range. On the otherhand, copper, cobalt, vanadium, bismuth, cadmium, mercury and cerium,will not extract as halides unless the pH of the medium is very acid,generally zero or less. For instance, at a pH of O, cobalt as a chloridewill extract in quantity, with the extractability decreasing rapidly atincreased pH levels. At a pH of 1.0 for example, virtually no cobaltcomes across, while gold, is rapidly extracted at a pH of 1.0 withslight agitation.

Conversion of the metal to the complex or salt may be accomplished asdesired. For example, treatment of gold bearing ore with aqua regia willdissolve the gold as AuCl, or HAuCl thus providing the gold in a formthat may be directly extracted after dissolution. Likewise, platinum maybe converted to the chloride by treatment of platinum containing mudwith aqua regia from direct extraction. Sea water, on the other hand,contains gold in solution as a chloride and requires no furthertreatment prior to the solvent extraction with the possible exception ofpH adjustment. It may be preferred, however, to concentrate sea water,even to a dry residue prior to the extraction. The solvent may then beslurried with a pass through the residue to ex-' tract the goldtherefrom. Further recovery may be made from scrap items. Scrap may bedissolved in aqua regia for gold, platinum, and the like, followed bydirect extraction. In certain situations, several precious metals may beextracted simultaneously from the scrap. In these cases, numerousconventional techniques may be employed for separating the extractedmetals. If, for

example, gold and platinum are simutaneously extracted from dissolvedscrap, the gold may be precipitated from the extract with hydroquinoneand the platinum remaining may be electrowon from the extract, or thelike.

Insofar as the particular complex or salt is concerned, obviously othersystems may be employed such as the remaining halides and the like.

The. particular medium containing the metal in extractable form, as setforth above may be liquid or solid. Economics of the operation maydetermine the proper form to be used. For example, sea water is currently being commercially evaporated by solar energy for the recovery ofsodium chloride. Treatment of the residue after evaporation will recoverthe gold contained therein without any extraction or dissolution of thesodium chloride. In mining operations, on the other hand, leach waterafter dissolution of the desired metal may be brought into contact withthe carbonate solvent according to the present invention, agitatedslightly and the metal quickly extracted therefrom with only slight, ifany, loss of solvent.

Depending upon the metal being extracted as well as the particular formthereof, and the presence of other metals in the medium, it may or maynot be desirable to adjust the pH of the medium. As mentioned above,gold as a chloride may be extracted over a wide pH range, while cobalt,copper, and the like will not be extracted as chlorides unless the pH ofthe medium is approximately zero or less. Hence pH adjustment of themedium may enable selective extraction of one metal from a group ofmetals that are present in the medium. At a pH of 1.0, for example, goldis very successfully extracted in approximately the 98 plus percentilewhile only trace quantities of iron, copper or the like are extracted.At a pH of 3.0, virtually no iron, copper or the like are extracted andthe gold is extracted in approximately the 98 percentile by multiplesolvent passes or extractions.

Once the metal has been solvent extracted and is present in the extract,it may be recovered by reducing the complex or salt to the pure metalform. Likewise, insoluble salts may be precipitated followed by furtherpurifications. Electro-winning is a convenient method for reduction ofthe metal, directly from the extract. In this regard, whileelectrowinning in certain circumstances is a slow and not particularlyefficient process, certain measures may be taken to vastly improve bothtime and efficiency. Electrowinning, in fact, is an extremely goodrecovery technique when the metal to be recovered is present inpropylene carbonate. Propylene carbonate has a dielectric constant of69.0 esu at 23C. and thus is quite suitable for the electrodeposition ofmetal therefrom. Further as mentioned herein the extract may be easilyconcentrated prior to recovery of the metal which also fosters theefficiency of the electrowinning process. Any other technique may alsobe employed which will precipitate or otherwise remove the metal fromthe extract. Electrodeposition may, however, be more feasible since thesolvent is virtually unaffected thereby. Electrodeposition of gold, forinstance, destroys a like amount of propylene carbonate as there is goldwon therefrom. In fact the operating efficiency for the carbonates ofthe present invention is in the neighborhood of 98 per cent for acarbonatecarrier mixture and 80 percent for propylene carbonate per se,though as mentioned earlier the dissolved propylene carbonate may berecovered. The carbonate solvent may thus be recycled for furtherextraction. Obviously if a diluent is utilized and flashed from themetal-pregnant extract, the volatilized diluent may be condensed andreclaimed for further use. There is thus little solvent that iscompletely lost during recovery of metals according to the presentinvention.

While propylene carbonate is approximately 20 per cent soluble in water,the addition of one of the diluents thereto reduces the solubility ofthe propylene carbonate. Also a saturated salt solution may be added tothe metal-containing medium which will tend to salt out the propylenecarbonate which again reduces the solubility of the propylene carbonate.

A mining process for gold will better illustrate the process of thepresent invention. Certainly the particular process for mining of otherof the metals may differ substantially from the gold process. The goldprocess is only exemplary, however, of the various processes.

Gold bearing ore is crushed or otherwise treated prepatory todissolution of the gold. The ore is then subjected to aqua regia, amixture of hydrochloric and nitric acids. The gold then dissolves andexists in the leach solution as AuClf or HAuCl Leach solution is thenadjusted to a pH of 0 to 3 by the addition of sodium hydroxide.Approximately 1 part of a propylene carbonate-benzene mixture rangingfrom about 5 to about 40 percent propylene carbonate is poured into theleach solution for each parts of leach solution. The solvent and leachsolution are then stirred slightly. Stirring is then stopped and thepropylene carbonatebenzene allowed to rise to the top of the vat. Theextract is then removed from the top of the vat, the benzene is flashedfrom the extract and the gold-pregnant carbonate is transferred to afurther vessel for electrodeposition of the gold in metal form. The goldis then electrodeposited onto a suitable electrode. Both the benzene andthe propylene carbonates may then be recycled into the system forfurther extraction. Likewise, depending upon the amount of solvent addedto the leach solution and the ratio of propylene carbonate to benzene,more than one extraction may be desirable to recover the gold present inthe leach solution.

A still better understanding of the present invention may be had byreference to the following specific examples.

EXAMPLE 1 A IOO-milliliter aliquota of an aqueous solution containing to230 mg of gold as gold (III) chloride was transferred to a separatoryfunnel. Five milliliters of saturated sodium chloride solution wereadded, the pH was adjusted to approximately 1.0 with sodium hydroxideand enough propylene carbonate added to give a 5-ml extract. The funnelwas shaken for about 15 seconds and the phases allowed to separate. Thepropylene carbonate layer (lower) exhibited a yellow color indicatingthe presence of gold and was then drained into a beaker. The extractionstep was repeated and the combined extracts dissolved in an excess ofwater. Analysis by an iodine-thiosulfate method showed that at least 98per cent of the gold was extracted. Gold was also extracted with atleast the same efficiency from additional solutions whose pH ranged fromabout 0.6 to about 3.0.

EXAMPLES 2-10 The procedure of Example 1 was repeated to ascertain theextractability of other metals as chlorides. These metals, the color ofthe extract and the pH range of the extractions are set forth in Table Ibelow.

Examples 210 thus illustrate how platinum could be extracted selectivelyfrom a solution containing platinum and cobalt by adjusting the pH ofthe solution above 0.

EXAMPLE l l A 100-milliliter aliquot of an aqueous solution containing20 mg each of cobalt, nickel, copper, zinc, iron, and mercury aschlorides and 130 to 230 milligrams of gold as its chloride wastransferred to a separatory funnel. Extractions and analyses wereperformed as in Example 1. At least 98 per cent of the gold wasextracted into the propylene carbonate layer, thus indicating that theother metals in solution with the gold did not interfere with theextraction.

EXAMPLES 1 2-22 One-hundred-milliliter solutions were made up containing150 milligrams of one of the metals listed in Table II. Extraction foreach of the metals was conducted as set forth in Example 1 followed byconventional analytical techniques for the particular metal, todetermine its presence in the extract. pH of the solutions in each casewas adjusted to 1.0.

TABLE II EXTRACI'ABILITY OF METALS AS CHLORIDES INTO PROPYLENE CARBONATEAT SOLUTION EXAMPLE 23 A IO-milliliter aliquot of aqueous solutioncontaining 25 mg. of gold as gold (III) chloride was transferred to aseparatory funnel. Two milliliters of saturated sodium chloride solutionwere added to the solution and the pH of the solution was adjusted to1.0, 5 milliliters of a mixture containing 5 volume per cent propylenecarbonate and 95 volume per cent benzene was added to the solution andthe funnel was shaken for about seconds. Gold extracted into thepropylene carbonatebenzene upper phase. The extract was separated fromthe aqueous phase and the benzene volatilized. The gold remained in theunvolatilized propylene carbonate.

EXAMPLES 24-37 Example 23 was repeated with the exception that the ratioof propylene carbonate to benzene or the diluent was changed, asindicated in Table III. In each case the gold extracted into the solventmixture as determined by visual observation of the color of the extract.

TABLE III EXTRACTION OF GOLD (III) CHLORIDE INTO PROPYLENECARBONATE-DILUENT SOLVENT Ex. No. Diluent %P.C. Extract Color 24 benzene10 Yellow 25 do 20 do 26 do do 27 do do 28 toluene do 29 o-xylene 50 do30 m-xylene 50 do 31 p-xylene 50 do 32 diethyl ether 50 do 334-methyl-2-pentanone 50 do 34 2,4-pentandione 50 do 35 ethyl acetate dodo 36 n-heptyl alcohol do do 37 chloroform do do EXAMPLES 38-46One-hundred-milliliter aliquots of aqueous solution containing 100 mg ofone of copper (11), copper (I), vanadium (V), gold (III), platinum (IV),uranium (VI), bismuth (III), cobalt (II), and cadmium (II) respectivelyas simple salts were transferred to separatory funnels. One gram ofpotassium thiocyanate was added to each and the pH of the solutionadjusted to values of O, 2, 3, 4, 6 and 8. Enough propylene carbonatewas added to each solution to give a 5-ml extraction. Extraction wasperformed as in Example 1 above. It was determined by colorimetry andconventional analytical methods that all the metal thiocyanate exceptbismuth were extracted almost completely from aqueous solution whose pHswere 0 to 3. Approximately 50 per cent of the bismuth was extracted inthis pH range. Cobalt was the only metal completely extracted at high pHvalues (greater than 6.0).

EXAMPLE 47 Example 1 was repeated with the exception that a solventmixture of 40 per cent ethylene carbonateper cent benzene was employedin lieu of the propylene carbonate solvent. The extract showed thepresence of gold, though extraction efficiency was less than with 4 Whatis claimed is:

1. A process for the solvent extraction of metal values selected fromthe group consisting of salts and complexes of gold, platinum,palladium, rhodium, iridium, cobalt, copper, vanadium, uranium, bismuth,cadmium, mercury, and cerium, comprising the steps of providing anaqueous medium containing at least one of the said metal values, saidmedium having an acid pH, and contacting said medium with a compositioncomprising a cyclic alkylene carbonate, said carbonate composition beingat lest partially insoluble in said medium.

2. A process as defined in claim 1 wherein the salt is a halide.

3. A process as defined in claim 2 wherein the halide is a chloride.

4. A process as defined in claim 1 wherein the cyclic alkylene carbonateis propylene carbonate.

5. A process as defined in claim 1 wherein the cyclic alkylene carbonateis ethylene carbonate.

6. A process as defined in claim 1 wherein the cyclic alkylene carbonatecomposition includes an organic liquid that is miscible with thecarbonate and is from only slightly soluble to insoluble in the medium.

7. A process as defined in claim 6 wherein the organic liquid isselected from the group consisting of benzene, o-xylene, m-xylene,p-xylene, diethyl ether, 4-methyl-2-pentanone, 2,4-pentandione, ethylacetate, n-heptyl alcohol, and chloroform.

8. A process as defined in claim 7 wherein the cyclic alkylene carbonateis propylene carbonate.

9. A process as defined in claim 7 wherein the cyclic alkylene carbonateis ethylene carbonate.

10. A process for the solvent extraction of a metal selected from thegroup consisting of gold, platinum, palladium, iridium and uraniumcomprising the steps of:

a. providing a halide of the metal to be extracted in a suitable aqueousmedium therefor;

b. adjusting the pH of the medium to a range of about -O.6 to about 3.0;

c. contacing the medium with a composition comprising an organicalkylene carbonate, said composition being at least partially insolublein said medium; whereby a phase separation occurs, the metal beinglocated in the carbonate phase;

d. separating the carbonate phase from the remainder of the medium; and

e. recovering the metal from the carbonate phase.

11. The process as defined in claim 10 wherein the metal is recoveredfrom the carbonate phase by an electrowinning process.

12. A process as defined in claim 10 wherein the carbonate is propylenecarbonate.

13. A process as defined in claim 10 wherein the carbonate is ethylenecarbonate.

14. A process as defined in claim 10 wherein the carbonate compositionincludes an organic liquid that is miscible with the carbonate and fromonly slightly soluble to insoluble in the medium.

15. A process as defined in claim 14 wherein the organic liquid isselected from the group consisting of benzene, o-xylene, m-xylene,p-xylene, diethyl ether, 4-methyl-2-pentanone, 2,4-pentandione, ethylacetate,

n-heptyl alcohol, and chloroform.

16. A process as defined in claim 14 wherein after the carbonate phaseis separated from the medium, the organic liquid is volatilized from thecarbonate prior to recovery of the metal therefrom.

17. A process as defined in claim 15 wherein the carbonate is propylenecarbonate which is present in the composition in a range of from about 5to about 40 per cent and the organic liquid is benzene which is presentin the range of from about to about 60 per cent.

18. A process as defined in claim 17 wherein the metal is recovered fromthe carbonate phase by electrowinning.

19. A process for the solvent extraction of a metal selected from thegroup consisting of gold, platinum, palladium, rhodium, iridium, cobalt,copper, vanadium, uranium, bismuth, cadmium, mercury, and cerium,comprising the steps of:

a. providing an aqueous medium of a thiocyanate of at least one of saidmetals;

b. adjusting the pH of the medium into the acid range;

c. contacting the aqueous medium with a composition comprising anorganic alkylene carbonate, said composition being at least partiallyinsoluble in said medium whereby a phase separation occurs, the metalbeing located in the carbonate phase;

d. separating the carbonate phase from the remainder of the medium; and

e. recovering the metal from the carbonate phase.

20. A process as defined in claim 19 wherein the metal is electrowonfrom the carbonate phase.

21. A process as defined in claim 19 wherein the carbonate is propylenecarbonate.

22. A process as defined in claim 19 wherein the carbonate is ethylenecarbonate.

23. A process as defined in claim 19 wherein the carbonate compositionalso includes an organic liquid in admixture therewith, said liquidbeing miscible with the carbonate and from only slightly soluble tocompletely insoluble in the aqueous medium.

24. A process as defined in claim 23 wherein the organic liquid isselected from a member of the group consisting of benzene, o-xylene,m-xylene, p-xylene, diethyl ether, 4-methyl-2-pentanone,2,4-pentandione, ethyl acetate, n-heptyl alcohol, and chloroform.

25. A process as defined in claim 24 wherein the carbonate is propylenecarbonate.

26. A process as defined in claim 24 wherein the carbonate is ethylenecarbonate.

27. A process as defined in claim 23 wherein prior to recovery of themetal from the carbonate phase, the organic liquid is volatilized fromthe carbonate composition.

28. A process as defined in claim 23 wherein the carbonate compositioncomprises from about 5 to about 40 per cent propylene carbonate and fromabout 95 to about 60 per cent benzene and the organic liquid.

29. A process as defined in claim 28 wherein the metal is removed fromthe carbonate phase by an electrowinning process.

1. A PROCESS FOR THE SOLVENT EXTRACTION OF METAL VALUES SELECTED FROMTHE GROUP CONSISTING OF SALTS AND COMPLEXES OF GOLD, PLATINUM,PALLADIUM, RHODIUM, IRIDIUM, COBALT, COPPER, VANADIUM, URANIUM, BISMUTH,CADMIUM, MERCURY, AND CERIUM, COMPRISING THE STEPS OF PROVIDING ANAQUEOUS MEDIUM CONTAINING AT LLEAST ONE OF THE SAID METAL VALUES, SAIDMEDIUM HAVING AN ACID PH, AND CONTACTING SAID MEDIUM WITH A COMPOSITIONCOMPRISING A CYLIC ALKYLENE CARBONATE, SAID CARBONATE COMPOSITION BEIGNAT LEAST PARTIALLY INSOLUBLE IN SAID MEDIUM.
 2. A process as defined inclaim 1 wherein the salt is a halide.
 3. A process as defined in claim 2wherein the halide is a chloride.
 4. A process as defined in claim 1wherein the cyclic alkylene carbonate is propylene carbonate.
 5. Aprocess as defined in claim 1 wherein the cyclic alkylene carbonate isethylene carbonate.
 6. A process as defined in claim 1 wherein thecyclic alkylene carbonate composition includes an organic liquid that ismiscible with the carbonate and is from only slightly soluble toinsoluble in the medium.
 7. A process as defined in claim 6 wherein theorganic liquid is selected from the group consisting of benzene,o-xylene, m-xylene, p-xylene, diethyl ether, 4-methyl-2-pentanone,2,4-pentandione, ethyl acetate, n-heptyl alcohol, and chloroform.
 8. Aprocess as defined in claim 7 wherein the cyclic alkylene carbonate ispropylene carbonate.
 9. A process as defined in claim 7 wherein thecyclic alkylene carbonate is ethylene carbonate.
 10. A process for thesolvent extraction of a metal selected from the group consisting ofgold, platinum, palladium, iridium and uranium comprising the steps of:a. providing a halide of the metal to be extracted in a suitable aqueousmedium therefor; b. adjusting the pH of the medium to a range of about-0.6 to about 3.0; c. contacing the medium with a composition comprisingan organic alkylene carbonate, said composition being at least partiallyinsoluble in said medium; whereby a phase separation occurs, the metalbeing located in the carbonate phase; d. separating the carbonate phasefrom the remainder of the medium; and e. recovering the metal from thecarbonate phase.
 11. The process as defined in claim 10 wherein themetal is recovered from the carbonate phase by an electrowinningprocess.
 12. A process as defined in claim 10 wherein the carbonate ispropylene carbonate.
 13. A process as defined in claim 10 wherein thecarbonate is ethylene carbonate.
 14. A process as defined in claim 10wherein the carbonate composition includes an organic liquid that ismiscible with the carbonate and from only slightly soluble to insolublein the medium.
 15. A process as defined in claim 14 wherein the organicliquid is selected from the group consisting of benzene, o-xylene,m-xylene, p-xylene, diethyl ether, 4-methyl-2-pentanone,2,4-pentandione, ethyl acetate, n-heptyl alcohol, and chloroform.
 16. Aprocess as defined in claim 14 wherein after the carbonate phase isseparated from the medium, the organic liquid is volatilized from thecarbonate prior to recovery of the metal therefrom.
 17. A process asdefined in claim 15 wherein the carbonate is propylene carbonate whichis present in the composition in a range of from about 5 to about 40 percent and the organic liquid is benzene which is present in the range offrom about 95 to about 60 per cent.
 18. A process as defined in claim 17wherein the metal is recovered from the carbonate phase byelectrowinning.
 19. A process for the solvent extraction of a metalselected from the group consisting of gold, platinum, palladium,rhodium, iridium, cobalt, copper, vanadium, uranium, bismuth, cadmium,mercury, and cerium, comprising the steps of: a. providing an aqueousmedium of a thiocyanate of at least one of said metals; b. adjusting thepH of the medium into the acid range; c. contacting the aqueous mediumwith a composition comprising an organic alkylene carbonate, saidcomposition being at least partially insoluble in said medium whereby apHase separation occurs, the metal being located in the carbonate phase;d. separating the carbonate phase from the remainder of the medium; ande. recovering the metal from the carbonate phase.
 20. A process asdefined in claim 19 wherein the metal is electrowon from the carbonatephase.
 21. A process as defined in claim 19 wherein the carbonate ispropylene carbonate.
 22. A process as defined in claim 19 wherein thecarbonate is ethylene carbonate.
 23. A process as defined in claim 19wherein the carbonate composition also includes an organic liquid inadmixture therewith, said liquid being miscible with the carbonate andfrom only slightly soluble to completely insoluble in the aqueousmedium.
 24. A process as defined in claim 23 wherein the organic liquidis selected from a member of the group consisting of benzene, o-xylene,m-xylene, p-xylene, diethyl ether, 4-methyl-2-pentanone,2,4-pentandione, ethyl acetate, n-heptyl alcohol, and chloroform.
 25. Aprocess as defined in claim 24 wherein the carbonate is propylenecarbonate.
 26. A process as defined in claim 24 wherein the carbonate isethylene carbonate.
 27. A process as defined in claim 23 wherein priorto recovery of the metal from the carbonate phase, the organic liquid isvolatilized from the carbonate composition.
 28. A process as defined inclaim 23 wherein the carbonate composition comprises from about 5 toabout 40 per cent propylene carbonate and from about 95 to about 60 percent benzene and the organic liquid.
 29. A process as defined in claim28 wherein the metal is removed from the carbonate phase by anelectrowinning process.